It was a totally unexpected turn of events. They always thought that Olivios was scary enough, until Marzu made his move. Only then everyone finally understood what was truly terrifying.
Aslan had finally been beaten fiercely. Their battle tactics and talents were not bad, but that was the problem.
Arbiters were also not lacking in talent. The important part was that they trained harder and had even trained to a point where it would be unbearable for most people. And on the battle experiences, they put more emphasis on the basics, to return to the basics.
Perhaps Arbiters were not especially popular or interesting, but they were definitely effective.